1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, a process cartridge and an image forming apparatus.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus has the following structure and processes. Specifically, an image-formed material is obtained by charging the surface of an electrophotographic photoreceptor by a charging unit in order to impart a desired polarity and a potential to the surface; forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor by selectively discharging the surface and exposing the surface to light in an image-wise manner; developing the latent image by attaching a toner thereto by a developing unit to form a toner image; and transferring the toner image onto an image-receiving medium by a transfer unit.
In recent years, the electrophotographic photoreceptor has become used more often in the fields of copy machines, laser beam printers and the like, because it has an advantage of providing high speed and high quality printing.
As the electrophotographic photoreceptor used in these image forming apparatuses, an electrophotographic photoreceptor (inorganic photoreceptor) using conventional inorganic photoconductive materials such as selenium, a selenium and tellurium alloy, a selenium and arsenic alloy, and cadmium sulfide has been known. In recent years, an electrophotographic photoreceptor (organic photoreceptor) using an organic photoconductive material, that exhibits excellent advantages in the low-cost productivity and disposability thereof, has become dominating a main stream.
A corona charging method utilizing a corona charging device has been conventionally used as a charging method. In recent years, however, a contact charging method, having such advantages as suppressed amounts of ozone production and electricity consumption, has been put to practical application and actively used. In the contact charging method, the surface of an electrophotographic photoreceptor is charged by bringing a conductive member serving as a charging member into contact with the surface of the electrophotographic photoreceptor, or by bringing the conductive member close to the surface of the electrophotographic photoreceptor, and then applying a voltage to the charging member. As the methods of applying a voltage to the charging member, there are a direct current method in which only a direct current voltage is applied, and an alternating current superposition method in which a direct current voltage is applied while superposing an alternating current voltage thereto. The contact charging method has such advantages as downsizing of the apparatus and suppressed generation of harmful gases such as ozone.
As a transfer method, a method of transferring a toner image onto a recording paper via an intermediate transfer member, which is applicable to a wide variety of recording paper, has been in wide use in place of a conventionally employed method in which a toner image is directly transferred onto a recording paper.
In the related arts described above, degradation and abrasion of the photoreceptor caused by using the contact charging method and also scratching and sticking of the photoreceptor caused by using the contact charging method and the intermediate transfer member have presented problems. In order to prevent these problems, a protective layer has been proposed to be formed on the surface of the electrophotographic photoreceptor so as to improve the strength thereof.